The invention relates to a method of treating cereal kernels (seeds) to decrease their mould content. The invention also relates to the treated cereal kernels, cereal kernel products made of them and to their use in malting, brewing, food and feed industry. The invention further relates to apparatuses for treating cereal kernels to decrease their mould content. More specifically, the method of the invention allows the mould content of the cereal kernels to be decreased without interfering with the germinability of the kernels. This is important particularly in the malting process of the kernels.
Moulds can be found everywhere in nature, e.g. in the soil and in the air, from where they spread to growing grain. Although moulds thus belong to the natural flora of grain, their wide occurrence is harmful because they may reduce the quality of grain and malt made thereof. For example, moulds can produce various mycotoxins detrimental to health. In addition, they may e.g. decrease the germinability of a kernel and the growth of germs, which is not only harmful for seed grain but also for malting of grain. It has also been shown that the beer brewed from heavily contaminated grain and malt tends to gush, which is a big problem for the brewing industry. Gushing is apparently due to metabolites produced by Fusarium and other moulds, which metabolites survive the process of brewing.
Kernels are exposed to moulds as soon as they are sown in the soil. The growth of mould is influenced by many factors, particularly moisture, temperature and time. Other significant factors are the supply of nutrients and oxygen and the competition between micro-organisms. Growing grain is predominated by so-called field fungi, the most common of which are Alternaria, Aureobasidium, Cladosporium, Epicoccum, Fusarium, Cochliobolus, Drechslera and Pyrenophora. Some of the field fungi are plant pathogens, the most harmful of which are Fusarium graminearum and F. culmorum. Also Cochliobolus sativus and Fusarium ssp. cause plant diseases and may be very harmful for the malting process. Humid weather during ear maturation and harvesting in particular presents favourable conditions for the growth of Fusarium moulds.
After harvest the grain should be dried rapidly to prevent the moulds from further reproduction. Field fungi cannot reproduce themselves in grain dried in an appropriate manner (approximately 12-13% moisture content) but they remain alive and reproduce themselves again, if they are exposed to humid conditions. Poorly stored grain is dominated by so-called storage fungi, i.e. Aspergillus and Penicillium, which survive in low moisture contents. Also storage fungi reduce the quality of grain and incur health risks both to those treating contaminated grain and to those consuming it.
When grain is malted, the moisture of the grain is increased again to 45-50% and the supply of oxygen is ensured, whereby the kernel starts germinating. The prevailing conditions during the process of malting are, however, not only suitable for the germination but also for the growth of moulds. A large amount of moulds is harmful for the process.
Malting aims at effecting physical, chemical and biochemical changes in the kernel. The malting process comprises three main stages: steeping, germination and kilning. First the cleaned and sieved grain is steeped in water to achieve the adequate moisture content. When the kernels have a sufficient moisture content, they are germinated at 13-16xc2x0 C. generally at least five days. This way, xe2x80x9cgreen maltxe2x80x9d is produced. Actual malt is produced by drying green malt under controlled conditions in which the temperature is slowly raised from about 45xc2x0 C. to about 85xc2x0 C., whereby the moisture content decreases approximately to four per cent. After drying, rootlets are eliminated, and they can be used as animal feed. Malt can also be processed into a malt extract for the food industry, for example.
Already at the stage of steeping during malting, the mould content of grain may rise, and it rises further at the stage of germination, Normal kilning of the malt does not substantially decrease the mould content of the kernels either.
Malt is mainly used for brewing beer, but also for the production of distilled spirits. Brewing comprises wort production, main and secondary fermentations and post-treatment. First the malt is milled, stirred into water and heated. During this xe2x80x9cmashingxe2x80x9d, the enzymes activated in the malting degrade the starch of the kernel into fermentable sugars. The produced wort is clarified, yeast is added, the mixture is fermented and a post-treatment is performed.
Many moulds are known to produce toxic compounds, i.e. mycotoxins, which may prejudice animal and human health. They may also harm malting and brewing. Thus, if there are a lot of moulds in the grain, the probability of mycotoxins is also higher. The most examined mycotoxins growing in grain originate from Fusarium, Cochliobolus sativus, Aspergillus and Penicillium moulds.
Several species of Fusarium moulds are not only pathogens of cereals but also potential sources of various mycotoxins. Particularly important mycotoxins are trichothecenes, zearalenone (ZEN) and its derivatives, fumonisins, moniliformin, fusarochromanones and fusaric acid. More than 100 different trichothecenes have been identified and characterized. Most attention has focused on Type A trichothecenes, including T-2 toxin, neosolaniol (NEO) and diacetoxyscirpenol (DAS) and on Type B trichothecenes, comprising deoxynivalenol (DON, i.e. vomitoxin) and its acetyl derivatives (3-ADON and 15-ADON), nivalenol (NIV) and fusarenon X. Fusarium mycotoxins and the factors affecting them are presented in J. P. F. D""Mello and A. M. C. Macdonald: Some Factors Affecting the Production of Fusarium Mycotoxins, p. 35-44, in:. J. P. F. D""Mello: Mycotoxins in Cereals: An Emerging Problem?, Handbook for fourth SAC Conference October 1996, Edinburgh.
In the chapter xe2x80x9cMycotoxins in Malting and Brewingxe2x80x9d of the above-mentioned work, B. Flanigan (p. 45-55) discusses the effects of mycotoxins on the malting and brewing industry. It is stated therein e.g. that the harmful effect of Cochliobolus sativus and Fusarium ssp. moulds on germinability is attributed at least in part to their production of mycotoxins, or other phytotoxic metabolites. Trichothecenes produced by Fusarium ssp. are inhibitory to the protein synthesis and thus reduce the production of alpha-amylase important for malting. Also the alpha-amino nitrogen concentrations in the wort decrease. Fusarium moulds may produce DON and zearalenone during malting. Grain and malt may also be contaminated with toxins produced by Penicillium verrucosum or Aspergillus clavatus causing allergic lung disease. T-2 toxin and other potent trichothecenes may retard fermentation, but although DON may be present in the wort, it has little effect on fermentation. Mycotoxins are not found in distilled spirits, but DON, nivalenol, fumonisins, aflatoxins, ochratoxin A and some other mycotoxins have been found in beer, but in low concentrations. Gushing of beer seems to correlate with zearalenone or DON. The health risk to humans from consuming mycotoxin contaminated beer is still uncertain, but the toxic effect of mycotoxins on farm stock fed on contaminated malting and brewing by-products is undisputed. For example, DON has been found in high concentrations in rootlets used as animal feed, and aflatoxins, zearalenones and ochratoxin A have been found in the mash waste.
Various solutions have been suggested to the problems relating to moulds in grain and malt. It is naturally worth aiming to dry the grain immediately after harvesting and to store it in dry. The growth of moulds can be retarded already in the field by spraying mould pesticides. Various cereals with a genotype resistant to e.g. Fusarium diseases have also been developed. Attempts have been made to reduce harmful effects of moulds in malting and brewing e.g. by supplying microbicidal substances, such as formaldehyde, into the steeping water. A large-scale use of formaldehyde is, however, forbidden for reasons of health. Any safe, generally acceptable chemical has not been found. Instead, the addition of lactic acid bacteria or preparations produced by them (WO94/16053) during the germination process has given good results. The effect of lactic acid bacteria of preventing the growth of moulds is apparently at least partly due to the microbicidal substances produced by them.
Surprisingly, a method of decreasing the mould content of cereal kernels with physical means has now been invented. The invention thus allows the reduction or avoidance of the above ill effects of moulds in a natural manner without the need for using chemical pesticides or other additives.
The present invention provides means for decreasing the mould content of cereal kernels without disturbing the germinability parameters of the grain. The invention thus enables the improvement of the quality of grain, particularly of grain to be malted and of seed grain. Along with the decrease in mould content, the invention also provides means for diminishing the harmful effects of moulds. The harmful effects that can be avoided by means of the invention include forming of mycotoxins, reduced germinability, reduced enzyme production, retarded growth of rootlets, retarded fermentation, gushing of beer and risks to animal and human health.
The method of the invention of treating cereal kernels (seeds) is characterized by exposing the kernels to heat at such a temperature and for such a period of time that the mould content of the kernels decreases but germinability remains, whereby the temperature of the kernels to be treated is raised to 60 to 100xc2x0 C. for 0.5 to 30 seconds. The cereal kernel of the invention is characterized in that it is treated with the method of the invention, and the cereal kernel product is characterized in that it is made of the cereal kernel of the invention. The invention also relates to the use of said cereal kernels in malting and the use of said cereal kernel products in brewing. An apparatus of the invention for treating cereal kernels is characterized in that it comprises transport means (1) to transport the cereal kernels, steam feeding means (2) to treat the cereal kernels with steam and air cooling means (3) to cool the cereal kernels with air, whereby the steam feeding means are adapted upstream of the air cooling means in the transport direction of the transport means. Another apparatus of the invention is characterized in that it comprises a feed box (14) to feed the kernels, a vertical pipe (13) containing a control cone (16) to disperse the kernels, and steam feeding means (19) to treat the kernels with steam. The preferred embodiments of the invention are disclosed in the dependent claims.
Cereal kernels are living material, which normally have to be treated gently so as to avoid affecting their viability. It is also well-known that moulds survive quite well the controlled heat treatment used in the kilning of green malt. Therefore it is surprising that the cereal kernels can be heat-treated in such a manner that their mould content decreases but their germinability is not weakened. In fact, the heat treatment described below was first tested on green malt, to which it was not suited, because the enzyme activity of the malt fell completely and the kernel xe2x80x9cdiedxe2x80x9d. Thus, it was not to be expected that the mould content of a non-malted cereal kernel can be minimised with a proper heat treatment without harming the viability of the kernel, such as germinability parameters, and vital enzymes, e.g. xcex1-amylase and xcex2-glucanase activities, which are important during germination.